Instrument Cluster

This is my first time posting to this forum so I hope I do this right. BTW thank you for the Happy Birthday greeting a few days ago although I would rather not count them anymore. My grand kids bought me a detail job on the interior of my 2000 XLT which desperately need to be cleaned. You know its dirty when the 3 and 7 year old grand kids get you a detail package. Now however, I’ve run into a problem which I hope someone can help me to resolve. When I turn on my headlights, the radio lights go so dim as to be almost invisible. It works perfectly with the headlights off. Further, the instrument cluster does not light at all. All of the indicators work, turn signals, seat belts etc, but the dash lights themselves fail to appear. I’ve check the fuse, 11 I believe if I can read the owner’s manual correctly and it is not blown. Oh yes, I’ve reseated the fuse to no avail.
Now my knowledge of electrical components is pretty much limited to the occasional shock and replacing light bulbs under careful supervision. Quite frankly I don’t know where to look next so I’m hoping someone can point me in the correct direction.

Thanks!
Bill